The tumor cell surface is currently a focus of active research, as it is believed that alterations at this site may not only account for the behavioral characteristics of tumor cells, but also trigger the immunological recognition and eradication of these altered cells. Avian oncornavirus transformed cells possess a tumor specific cell surface antigen (TSSA), which has been biochemically characterized as a 100,000 dalton glycoprotein (gp100 TSSA). A detailed biochemical and immunological understanding of this molecule would contribute significantly to the present information regarding the mechanism of transformation. With this objective in mind, we plan to: 1) Isolate and biochemically characterize the TSSA molecule. 2) Investigate whether TSSA could be a viral coded product of an oncornavirus gene that is expressed in transformed cells. 3) Examine the possible functions associated with the TSSA, such as enzymatic, recognitive, or regulatory activities. 4) Examine by in vitro cellular and humoral cytotoxicity the role of TSSA in eliciting the immunological destruction of oncornavirus transformed cells.